Tensorflow in Scala reflection

问题

I am trying to get tensorflow for java to work on Scala. I am use the tensorflow java library without any wrapper for Scala.

At sbt I have:

If I run the HelloWord found here, it WORKS fine, with the Scala adaptations:

import org.tensorflow.Graph
import org.tensorflow.Session
import org.tensorflow.Tensor
import org.tensorflow.TensorFlow


val g = new Graph()
val value = "Hello from " + TensorFlow.version()
val t = Tensor.create(value.getBytes("UTF-8"))
// The Java API doesn't yet include convenience functions for adding operations.
g.opBuilder("Const", "MyConst").setAttr("dtype", t.dataType()).setAttr("value", t).build();

val s = new Session(g)
val output = s.runner().fetch("MyConst").run().get(0)

However, if I try to use Scala reflection to compile the function from a string, it DOES NOT WORK. Here is the snippet I used to run:

import scala.reflect.runtime.{universe => ru}
import scala.tools.reflect.ToolBox
val fnStr = """
    {() =>
      import org.tensorflow.Graph
      import org.tensorflow.Session
      import org.tensorflow.Tensor
      import org.tensorflow.TensorFlow

      val g = new Graph()
      val value = "Hello from " + TensorFlow.version()
      val t = Tensor.create(value.getBytes("UTF-8"))
      g.opBuilder("Const", "MyConst").setAttr("dtype", t.dataType()).setAttr("value", t).build();

      val s = new Session(g)

      s.runner().fetch("MyConst").run().get(0)
    }
    """
val mirror = ru.runtimeMirror(getClass.getClassLoader)
val tb = mirror.mkToolBox()
var t = tb.parse(fnStr)
val fn = tb.eval(t).asInstanceOf[() => Any]
// and finally, executing the function
fn()

Here simplified build.sbt to reproduce the error above:

lazy val commonSettings = Seq(
    scalaVersion := "2.12.10",

    libraryDependencies ++= {
      Seq(
                  // To support runtime compilation
        "org.scala-lang" % "scala-reflect" % scalaVersion.value,
        "org.scala-lang" % "scala-compiler" % scalaVersion.value,

        // for tensorflow4java
        "org.tensorflow" % "tensorflow" % "1.15.0",
        "org.tensorflow" % "proto" % "1.15.0",
        "org.tensorflow" % "libtensorflow_jni" % "1.15.0"

      )
    }
)

lazy val `test-proj` = project
  .in(file("."))
  .settings(commonSettings)

When running the above, for example with sbt console, I get the following error and stack trace:

java.lang.NoSuchMethodError: org.tensorflow.Session.runner()Lorg/tensorflow/Session$$Runner;
  at __wrapper$1$f093d26a3c504d4381a37ef78b6c3d54.__wrapper$1$f093d26a3c504d4381a37ef78b6c3d54$.$anonfun$wrapper$1(<no source file>:15)

Please ignore the memory-leaks that the previous code has given that no resources context (to close()) is used

回答1:

The thing is in this bug appearing in combination of reflective compilation and Scala-Java interop

https://github.com/scala/bug/issues/8956

Toolbox can't typecheck a value (s.runner()) of path-dependent type (s.Runner) if this type comes from Java non-static inner class. And Runner is exactly such class inside org.tensorflow.Session.

You can run the compiler manually (similarly to how Toolbox runs it)

import org.tensorflow.Tensor
import scala.reflect.internal.util.{AbstractFileClassLoader, BatchSourceFile}
import scala.reflect.io.{AbstractFile, VirtualDirectory}
import scala.reflect.runtime
import scala.reflect.runtime.universe
import scala.reflect.runtime.universe._
import scala.tools.nsc.{Global, Settings}

val code: String =
  """
    |import org.tensorflow.Graph
    |import org.tensorflow.Session
    |import org.tensorflow.Tensor
    |import org.tensorflow.TensorFlow
    |
    |object Main {
    |  def foo() = () => {
    |      val g = new Graph()
    |      val value = "Hello from " + TensorFlow.version()
    |      val t = Tensor.create(value.getBytes("UTF-8"))
    |      g.opBuilder("Const", "MyConst").setAttr("dtype", t.dataType()).setAttr("value", t).build();
    |
    |      val s = new Session(g)
    |
    |      s.runner().fetch("MyConst").run().get(0)
    |  }
    |}
""".stripMargin

val directory = new VirtualDirectory("(memory)", None)
val runtimeMirror = createRuntimeMirror(directory, runtime.currentMirror)
compileCode(code, List(), directory)
val tensor = runObjectMethod("Main", runtimeMirror, "foo").asInstanceOf[() => Tensor[_]]
tensor() // STRING tensor with shape []

def compileCode(code: String, classpathDirectories: List[AbstractFile], outputDirectory: AbstractFile): Unit = {
  val settings = new Settings
  classpathDirectories.foreach(dir => settings.classpath.prepend(dir.toString))
  settings.outputDirs.setSingleOutput(outputDirectory)
  settings.usejavacp.value = true
  val global = new Global(settings)
  (new global.Run).compileSources(List(new BatchSourceFile("(inline)", code)))
}

def runObjectMethod(objectName: String, runtimeMirror: Mirror, methodName: String, arguments: Any*): Any = {
  val objectSymbol = runtimeMirror.staticModule(objectName)
  val objectModuleMirror = runtimeMirror.reflectModule(objectSymbol)
  val objectInstance = objectModuleMirror.instance
  val objectType = objectSymbol.typeSignature
  val methodSymbol = objectType.decl(TermName(methodName)).asMethod
  val objectInstanceMirror = runtimeMirror.reflect(objectInstance)
  val methodMirror = objectInstanceMirror.reflectMethod(methodSymbol)
  methodMirror(arguments: _*)
}

def createRuntimeMirror(directory: AbstractFile, parentMirror: Mirror): Mirror = {
  val classLoader = new AbstractFileClassLoader(directory, parentMirror.classLoader)
  universe.runtimeMirror(classLoader)
}

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来源：https://stackoverflow.com/questions/60783153/tensorflow-in-scala-reflection

标签

scala

tensorflow

scala-reflect